1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device having an output element formation region, an other element formation region, and an active barrier region arranged between the output element formation region and the other element formation region.
2. Description of the Background Art
In products used for automobiles, motor drive, audio amplifiers, and the like, an L (self inductance) load sometimes produces counter-electromotive force to cause the drain (n-type region) of an output transistor to have a negative potential. In this case, the negative potential allows electrons to be injected from the drain to a p-type substrate and move from an output transistor formation region to an other element formation region through the p-type substrate, causing the other elements to malfunction. To solve this problem, an active barrier region may be formed between the output transistor formation region and the other element formation region.
This active barrier region is formed such that a p-type region and an n-type region having a floating potential are ohmic-connected through a conductive layer, as disclosed in the following document: A. R. Stella, et al., “Novel achievements in the understanding and suppression of parasitic minority carrier currents in P− epitaxy/P++ Substrate Smart Power Technologies,” Proceedings of 2004 International Symposium on Power Semiconductor Devices & ICs, Kitakyushu, pp. 423-426.
More specifically, electrons injected into a p-type substrate disappear in the p-type substrate due to recombination or are taken into the n-type region of the active barrier region. Since electrons are taken into the n-type region of the active barrier region, the n-type region attains a positive potential. When the n-type region attains a positive potential, the p-type region of the active barrier region attains a negative potential in order to cancel this, because the p-type region and the n-type region having a floating potential are ohmic-connected through the conductive layer in the active barrier region. When the p-type region of the active barrier region attains a negative potential, the electrons injected into the p-type substrate hardly move forward from the p-type region having a negative potential. Therefore, electrons hardly reach the other element formation region from the active barrier region, preventing a malfunction of the other elements.
However, in conventional semiconductor devices, the active barrier region and the output transistor formation region as well as the active barrier region and the other element formation region are electrically isolated from each other by a pn junction. In the isolation structure using this pn junction, impurity diffusion in the impurity diffusion region forming the isolation structure inevitably increases the size of the isolation structure, so that the chip size cannot be decreased.
In addition, in the isolation structure using a pn junction, the effect of preventing the movement of electrons from the output transistor formation region to the other element formation region is not enough.